1. Field of the Invention
The present invention relates generally to the field of printer ink cartridges and, more specifically, to printer ink cartridges which contain a portion of the drive control logic to operate the jet nozzles on the cartridge.
2. Description of the Related Technology
Ink cartridges are used in ink jet printers, a class of noncontact printers characterized by rapid heating and expulsion of ink from nozzles onto paper. Many printer ink cartridges are passive devices, i.e., use passive components on a jet plate assembly, such as resistors to heat the ink in the cartridge, to a point that it will expel from jet nozzles or openings in the jet plate.
The resistors are formed utilizing thick or thin film technology on a substrate. Typically, one resistor per orifice or jet is required. These passive printer ink cartridges are "dumb" devices because they require an interface to control and driver circuitry on the printer to determine when each nozzle on the cartridge is to be fired. The printer sends control signals to the resistors on the cartridge to control the firing sequence of the jets as the cartridge moves along the page.
One of the first printer ink cartridges that used this passive design was designed by Hewlett-Packard in approximately 1984 and was sold under the trade name ThinkJet Cartridge. The ThinkJet Cartridge had 12 jet nozzles and required 13 interconnect lines to the printer system to control the application of ink by the cartridge. The design and operation of the ThinkJet cartridge is described in more detail in an article entitled, "History of ThinkJet Printhead Development", published in The Hewlett-Packard Journal dated May 1985.
In approximately 1987, Hewlett-Packard developed the DeskJet thermal printer inkjet cartridge which increased the number of jets on the printer ink cartridge to fifty. However, the Deskjet Cartridge is also a passive device that requires an interface to control and driver circuits on the printer to activate the jets. The DeskJet cartridge has fifty jets and requires fifty-six interconnect lines to the printer system to control the application of ink by the cartridge. The design and operation of the original DeskJet cartridge is described in more detail in an article entitled, "Low Cost Plain Paper Printing," published in The Hewlett-Packard Journal dated August 1992.
Recently, Hewlett-Packard designed a thermal printer ink cartridge, Part No. HP51640, used in a DeskJet 1200 printer also by Hewlett-Packard which incorporated a portion of the driver electronics and some control logic onto the jet plate of the printer ink cartridge. In this particular case, the jet plate is composed of the following structures: (1) a silicon substrate which houses the driver control circuitry for each jet, (2) some control logic circuitry to determine which jet is to be fired, and (3) the heat generating resistors. Since the driver control circuitry and the control logic circuitry is proximate to the heat generating resistors, the driver control logic circuitry is susceptible to the heat generated by the heat generating resistors. The jet plate is located proximate to the jet nozzles to heat the ink for expulsion. The design and operation of the DeskJet 1200 cartridge is described in more detail in two articles entitled, "The Third-Generation HP Thermal InkJet Printhead" and Development of the "HP DeskJet 1200C Print Cartridge Platform" published in The Hewlett-Packard Journal dated February 1994.
In addition, Canon has incorporated the driver circuitry and some control logic circuitry on the jet plate assembly in their BubbleJet BJ-02 cartridge, which was developed for use with the BubbleJet printer. The jet plate assembly on the BubbleJet cartridge is basically an aluminum plate which acts as a heat sink, a PC board, and a silicon substrate. The silicon substrate comprises some driver circuitry, some logic circuitry, and the heat generating resistors. The heat generating resistors are encapsulated and form little cave-like channels such that the ink is directed into the channels and then ejected through the process of heating the ink and causing bubbles to eject the ink across the silicon substrate. Since the ink comes into contact with the silicon substrate, the substrate must be protected by a barrier layer which is not effected by the chemicals in the ink.
As is known to those of skill in the art of silicon circuit fabrication, the larger the circuit that is produced on a silicon substrate, the harder the circuit is to manufacture. In addition, as the size of the circuit increases, the yield of operable circuits that are produced decreases. Further, as the circuit size increases, the potential for long term reliability problems increases. Therefore, the manufacturing costs rise dramatically with the increased size of the circuit that is produced on silicon.
In the case of developing a silicon integrated circuit on a jet plate to drive and control the operation of the jets, a number of factors directly affect the size of the circuitry required. Initially, each jet nozzle requires one heating element, such as a resistor, one drive control circuit and one or more control signals to indicate when the jet nozzle is to be fired. As the number of jets increase, the size of the silicon substrate required to house the driver circuits, control circuits and the heating elements increases proportionally to the number of added jets. Also, the increased number of jets, for example 84 jets, requires a silicon die having an inefficient shape or having a large aspect ratio, i.e., a die having a long length and a short width, because the increased number of jets causes the die to increase in length. Both large dies and dies with a large aspect ratio are very difficult to manufacture, further decreasing processes yields and increasing production costs.
In addition to the problems of silicon yield for such large circuits, the circuitry on the jet plate must be able to withstand the heat generated by the resistors as well as problems associated with silicon coming into constant contact with moving heated ink. Therefore, the production of the silicon integrated circuit on the jet plate must include additional steps to prevent long-term degradation of the silicon due to contact with the chemicals in the ink, to cavitation problems caused by the moving ink, etc. These processes increase the production costs for making a jet plate. These same processes may also decrease the performance characteristics of the driver and logic circuits on the jet plate.